This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Spinal muscular atrophy (SMA) is a neuromuscular disease characterized by degeneration of motor neurons and progressive muscle atrophy. The disease is one of the most common genetic causes of infant death. Deletion or mutation(s) of the survival motor neuron gene (SMN1) causes the disease. The SMN protein has been known to function in the assembly of the RNA splicing complex;however, the mechanism(s) by which SMN-deficiency causes cell death in SMA are not clear. Our long-term goal is to understand the mechanism(s) of motor neuron death in SMA and develop a means of prevention. SMN protein has been reported to have some survival-promoting functions in cultured cells. Our studies showed that skin fibroblasts derived from SMA patients are more sensitive to certain death-promoting stimuli than control fibroblasts. We hypothesize that the SMN protein is directly involved in cell survival and that loss of SMN?s survival function results in motor neuron death in SMA. We have used skin fibroblasts derived from SMA patients and PC12 cells as model systems to test this hypothesis. We found that SMA fibroblasts are more prone to camptothecin?induced cell death. Camptothecin treatment results in significant higher caspase-3 activity in SMA fibroblasts, and levels of SMN protein are inversely associated with caspase-3 activity induced by camptothecin. We also demonstrated that transient expression of human SMN in both na[unreadable]ve and differentiated PC12 cells decreased camptothecin?activated caspase-3 activity. Upon camptothecin treatments, levels of p53 protein are elevated, suggesting SMN may play its survival function through pathway(s) that are involved in p53. We are currently investigating the effect of SMN on p53 -induced death in PC12 cells. We will further elucidate the role of SMN in motor neuron survival. Finally, we will continue to determine biological pathway(s) of SMN-mediated cell protection.